Governmental legislation requires the development of a system capable of sensing information related to front passenger seat occupants and classifying such occupants to the extent necessary to adapt airbag deployment to improve passenger safety. For example, airbag deployment can be a problem for small children or children in car seats occupying a front passenger seat. Using information provided by vehicular seat weight sensors, a control system can override the normal airbag actuation mechanism and prevent airbag deployment when such child occupies a seat having appropriate weight sensors. In other situations, airbag deployment can remain active but its intensity can be modulated in response to sensed weight information, for example, when the occupant is incorrectly positioned or is within some intermediate weight classification.
Vehicular weight sensors in such a system would be disposed, for example, between a first frame or riser attached to the chassis of the vehicle and a second frame that supports the seat. In the case of movably mounted passenger seats, the second frame typically comprises an upper track adjustably movable on a lower track with the seat structure mounted on the upper track. Sensors can also be mounted between an upper track and a side member.
An example of a suitable weight sensor is shown and described in copending application Ser. No. 10/874,963 filed Jun. 23, 2004 claiming the benefit of Provisional Application No. 60/491,417, filed Jul. 31, 2003 and assigned to the assignee of the instant invention, the subject matter of which is incorporated herein by this reference. Such weight sensors have, inter alia, a first body formed with a sense surface on which strain sensors are disposed and have a mounting post extending away from the first body. A second body is provided with a tubular wall, the distal free end of which is attached to the first body around the perimeter of the sense surface and has a second mounting post extending away from the second body in a direction opposite that of the post of the first body generally along a common longitudinal axis. Essentially, weight is transmitted as a force to the first body creating a strain on the sense surface.
Performance of the weight sensors of the type described in the above referenced application is directly related to parasitic loads at the interface of the sensors with surrounding components such as the track, riser and the like. By way of example, the tracks on opposite sides of the seat may be somewhat out of parallel with each other even when they are within specified tolerances and this can place a moment on the sensors creating a parasitic stress that affects the sensor output.